One and one make two. Right? Well, not necessarily, at least not when architect Allan Greenberg and designer Elissa Cullman are doing the math. “If you really work well with your interior designer, one and one make three,” says Greenberg. “The architect and the designer both have their own thoughts, and they both bring their own intelligence to the project. If you can combine the two of them, there’s a bonus.”

The proof of that happy equation is on view in a new Georgian-style house, set on 100 acres in New Jersey’s horse country, a little more than an hour from Manhattan. The owners—the husband is an investment banker, and the wife is a venture capitalist—wanted a house that looked as if it had been there for 150 years, but they didn’t want 150-year-old problems. Brick Georgian was their preferred style, and that led them to Greenberg, who is, in the wife’s opinion, “the absolute dean of Georgian architecture in the United States.”

The owners wanted a house that looked as if it had been there for 150 years, but they didn’t want 150-year-old problems.

The couple already knew and admired Cullman and Jenny Fischbach, her senior designer. Together, the two women had done the interiors of their Nantucket getaway (see Architectural Digest, November 2007) and their previous home in New Jersey. Cullman and Fischbach have a sense of how the family lives, says the wife—the couple have two teenage sons—and they know how to make a traditional home warm and livable. That is a valuable talent in the design of a 16,000-square-foot house with 25 rooms, including three separate dining areas—a formal dining room, an intimate dining room and a breakfast room.

Such a large house demands a grand entrance, and Greenberg provided it with a sequence of three rooms, each with a different shape, leading from the front door: a square foyer at the door itself, a larger elliptical hall and, finally, a long stair hall on the cross axis. “It’s the most exciting sequence of three spaces that we’ve ever worked on,” says Cullman.

“A strong geometry is a key element of this house, and a variety of shapes pulls you through it from room to room,” says Greenberg, whose architectural hero, the 18th-century Scottish architect Robert Adam, also used ingenious configurations to create some of Britain’s finest Georgian houses, including the recently restored Dumfries House (see Architectural Digest, April 2008). In an ebullient Adam-like geometric display in the 21st century, Greenberg created such things as barrel-vaulted ceilings, domed ceilings and two octagonal rooms at either end of the house.

“A perfect trifecta,” Fischbach calls the combination of architect, clients and designers. Though Greenberg was indisputably the architect, and Cullman and Fischbach were without question the interior designers, collaboration was so close that Greenberg helped with their interior and Cullman and Fischbach had a hand in his architecture. In almost every room, Greenberg made a slight architectural adjustment to accommodate their interior design. The designers thought that they needed an extra-long sofa to sit comfortably in the large living room, for instance. Could he lengthen the wall? they asked him. “A lesser architect would have said, ‘I like it this way. Buy a smaller sofa,’ ” says Cullman. “Allan just said: ‘Your wish is my command.’ ”

“I believe that a house is more of a home by being a work of art,” says Greenberg, and the art of this house can be seen everywhere, from the lunettes over the entrance doors to the intricate black-and-white patterns on the limestone floor to the sinuous—and sensuous—flying staircase at one end of the main hallway. “You couldn’t ask for a more dramatic staircase,” says Cullman.

Cullman and Fischbach employed both drama and calm. Calm is evident in the regal master bedroom, with its yellow Venetian plaster walls, and in the living room, whose walls are what Cullman calls a toasty beige. “We knew our clients were collecting contemporary art,” she says, “and we had to make the walls neutral. We never choose colors in our office in New York. The real fun is mixing in the room to make it perfect for that location.”

High drama they saved for the formal dining room, which can only be described as sumptuous. To illuminate it they chose a spectacular ormolu-and-cut-glass Empire chandelier with 15 sparkling lights. “We think chandeliers are the forgotten children of decorating,” says Cullman, “and we search the world for them. When people use downlights, the ceilings are gray. With the proper chandelier, you get a glow that makes the whole ceiling light and happy.” Even more spectacular is the hand-painted 18th-century Chinese wallpaper, the best example of its kind, says Cullman, in private hands in the United States. “This wallpaper is every bit as good as any you would find in the Metropolitan Museum or Winterthur,” she says. “It’s as good as it gets.”

As good as it gets is how the clients see their entire house. “Every day,” says the wife, “I marvel at the details and the care put into it.” Perhaps Greenberg will have to revise his equation so that, on occasion, one and one actually make four.